1. Field of the Invention
The present invention relates to a reflective liquid crystal display apparatus and, more particularly, to an improvement in a reflective plate of a reflective liquid crystal display apparatus.
2. Description of the Prior Art
A reflective liquid crystal display apparatus does not require a back light as a light source because light obtained by reflecting external incident light by a reflective plate positioned inside the liquid crystal display apparatus is used as a display light source. This apparatus is considered to be an effective system for achieving a decrease in power consumption, a decrease in thickness, and a light weight, compared to a transparent liquid crystal display apparatus. The basic structure of a conventional reflective liquid crystal display apparatus comprises a liquid crystal of a TN (Twisted Nematic) scheme, an STN (Super Twisted Nematic) scheme, a GH (Guest Host) scheme, a PDLC (macromolecular dispersion) scheme, or the like, elements (e.g., thin film transistors or diodes) for switching the liquid crystal, and a reflective plate arranged on the inner or outer side of the elements.
The display performance of the reflective liquid crystal display apparatus is required to provide a bright, white display in a liquid crystal transmissive state. To realize this display performance, it is important to control the reflective properties of the reflective plate.
The surface of a conventional reflective plate is corrugated to reflect light incident at all angles by a reflective surface in a target direction (display direction).
Well-known corrugation shapes on the surfaces of reflective plates are as follows.
1 The pitch of corrugations falls within a range of 1 .mu.m to 100 .mu.m, the corrugation height falls within a range of 0.1 .mu.m to 10 .mu.m, the corrugation inclination angle is 0.degree. to 30.degree. with respect to the horizontal surface of a substrate, and intervals between the projecting portions of the corrugations are irregular (disclosed in Japanese Examined Patent Publication No. 61-6390).
2 The corrugation height exhibits the Gaussian distribution, and the average inclination angle of corrugations at this time is 10.degree. (disclosed in Tohru Koizumi and Tatsuo Uchida, Proceedings of the SID, Vol. 29, 157, 1988).
3 The surface of a reflective electrode has a plurality of projecting portions arrayed irregularly (disclosed in Japanese Unexamined Patent Publication No. 6-75237).
4 The surface of a reflective plate is a smooth corrugated surface, and the average inclination angle of corrugations is selected from 4.degree. to 15.degree. (disclosed in Japanese Unexamined Patent Publication No. 6-175126).
5 At least two or more projecting portions having different heights are formed on the surface of a reflective plate (disclosed in Japanese Unexamined Patent Publication No. 6-27481).
A conventional method of corrugating a reflective plate uses photolithography and etching which are performed to an organic film to uniformly corrugate a large-area substrate without causing any damage. To obtain a reflective plate having desired reflective properties, a corrugation shape on the surface of the reflective plate must be optimally designed.
In the above references of the reflective liquid crystal display apparatuses, the average inclination angle of corrugations is designated to optimize a corrugation shape. As for practical reflective performance, however, a flat region is included in the corrugation shape on the entire surface of the reflective plate, or corrugated surfaces having various inclination angles except for the inclination angle designated in the reference are present on the entire surface of the reflective plate. For this reason, it is difficult to obtain a bright reflective liquid crystal display apparatus having a reflective plate by designating only the average inclination angle described in the references.
In the above references, the surface of the reflective plate is irregularly corrugated. However, these references are insufficient for defining a corrugated structure on the surface of the reflective plate having optimum reflective performance because designation of a detailed irregular shape is indefinite, and irregularity from a regular structure is not defined.